1. Field of the Invention
The present invention relates to an imaging device whose gain is set to achieve high S/N and an exposure control method for the imaging device.
2. Description of the Related Art
There has been proposed an image sensor that uses white (gray) pixels for coding. White balance in signal processing in an image sensor is typically carried out with reference to green pixels. However, color coding including white (gray) pixels causes the following various problems because the white (gray) pixels will be saturated earlier than other color filters. One of the problems is reduced linearity after signal processing. When correlation of white pixel signals is used to generate a chrominance signal and a luminance signal, the chrominance signal and the luminance signal fail in the saturated region. Another problem is that although white pixels contribute as a luminance signal component, saturation of white pixels earlier than other color pixels causes reduced resolution and a lower dynamic range. Color coding including white (gray) pixels for improving the sensitivity of an image sensor has been proposed (see Re-publication of PCT patent application WO2002/056603, for example).